Heretofore, point light sources such as an incandescent lamp, a tungsten lamp and so forth have commonly been used.
Exposure devices using the point sources have had such a disadvantage that an exposure unevenness has been apt to occur between the center and the corners of an image. With the purpose of covering the disadvantage, a complicated optical system has been used or a spatial distance has been provided between a light source and an irradiative surface so as to change, as much as possible the light emitted from the point source into a light as if it were emitted from a surface light source. Nevertheless, a device has been unavoidable to be enlarged in size. Further, the point sources such as an incandescent lamp, a tungsten lamp and so forth have a possibility to be cut off suddenly in use, due to the expiration of life. If this is the case happened in a hospital, for example, medical films are developed without printing any ID marks such as patients' names, so that there raises a serious problem that a subject patient cannot be identified later by the developed film, and vice versa.